Such a force-storing unit is already known from German patents 1,956,369 and 2,806,282. This type of force-storing unit serves for the snap actuation of a load switch of a tap changer; it is loaded, effectively wound up, at the start of each actuation of the tap changer by its drive shaft. It is formed mainly as a force-storing slide and an output part that is often called the snap slide, between which there are one or more springs serving to store force.
The force-storing slide is thus moved linearly by an eccentric on the drive shaft relative to the output part so that the force-storing springs between them are tensioned. Once the force-storing slide reaches its new end position, the output part is unblocked and is thereby released. It is moved very suddenly to follow the linear movement of the force-storing slide since the force-storing springs were previously loaded. This snap-action linear movement of the output part is converted by a slider and a crank into rotation of a drive shaft. The fast-moving output shaft in turn serves for actuating the load switch of the tap changer, that is to switch between the previous and newly selected winding under load.
This known force-storing unit has however several disadvantages. The conversion of the linear movement of the output shaft via a slider and a tie rod and crank into a rotation of the output part results in a nonuniform force transmission or movement conversion. In addition as a result of this type of movement conversion and the practicable lever relationships of the crank, the resulting rotation angle of the output shaft for each switching is fairly limited. In practical embodiments of the known force-storing unit this angular movement is about 75 degrees. Such an angular movement is further limited by the maximum possible switching time which is available for the actuation of a load switch, that is for the uninterrupted changeover. For many load switches, in particular with switches that operate a plurality of contacts with each actuation, e.g. both mechanical contacts and vacuum switches, one after the other in a particular sequence, the known force-storing unit does not have enough angular movement to effect the desired movement. Finally the known force-storing units are fairly bulky since the force-storing slide, force-storing springs, and output part are provided one above the other in different horizontal planes.
German 199 13 814 describes how an output part of a force-storing unit of this type has on both of its longitudinal side an inwardly directed row of teeth in which, dependent on the movement direction of the output part, can engage selectively a gear carried on the output shaft. This known arrangement serves also, independently of the direction the force-storing unit is tensioned, to urge the output shaft always in the same direction so that a special additional device is needed to switch the gear wheel between opposite sides of the longitudinal rows of teeth. This makes the force-storing unit also quite complicated and takes up even more space than was necessary in the prior art.